The present invention relates to a seal mechanism in gear pumps or motors of a type such that it includes a pressure plate partitioned with a figure-3 shaped seal member at the back into a high pressure zone and a low pressure zone. Furthermore, in detail, the present invention relates to an improved seal mechanism of this type that facilitates the assembly work of gear pumps or motors without permitting either of the end parts of the figure-3 shaped seal member disposed at the back of the pressure plate to exert any substantial initial pressure on the inner wall surface of the gear bower in the housing in the assembly work during the operation of the gear pump or motor, permits the liquid pressure in the high pressure zone of the pressure plate to press both end parts of the said seal member to the inner wall surface of the gear bower so as to prevent completely the leakage of any liquid leak from these parts.
In general, for gear pumps or motors, the following two types of seal mechanism are known. One is seen, for instance, in Specifications of U.S. Pat. Nos. 3,539,282, 3,891,360 and 4,029,446 incorporates a pair of mutually engaging gears, each shaft of which is supported, rotating freely, by a bearing block inserted movably against the gear bower in the housing, while the other is seen, for instance, in U.S. Pat. Nos. 3,270,680, 3,473,476 and 3,890,068, incorporates a pair mutually engaging gears, at least one side of which is in contact with a pressure plate, movable along the direction of the shaft, each of the gear shafts being supported by a fixed bushing fitted in the end wall of the housing or the end cover. In either of these types, the said bearing block or pressure plate is partitioned at the back with a figure-3 shaped seal member into a high pressure zone and a low pressure zone so that, during the operation of the gear pump or motor, a proper balance may be kept between the liquid pressures acting on both sides of the bearing block or the pressure plate and so that the gear side surface may be sealed completely.
In relation to gear pumps or motors of the latter type, described above, that include a pressure plate and particularly with reference to the assembly formed by inserting the end surface of each bushing fitted in the end cover into the shaft hole of the said pressure plate as seen in Specification of U.S. Pat. of 2,809,592, the present invention has been developed to facilitate the assembly work while securing reliable sealing.
Namely, in gear pumps or motors of this type, if an initial tension is imparted to both end parts of the figure-3 shaped seal members during assembly, so as to secure the required sealing performance, the figure-3 shaped seal members may be deformed due to this initial tension when they are fitted in the gear bower of the housing. Therefore, when the end cover is fitted to the housing, there is a danger that the end of the bushing fitted in the said end cover may interfere and impair the deformed seal member, degrading its sealing performance. Thus, the assembly work requires careful attention and particular skill. In order to simplify the assembly work, therefore, it is not advisable to impart an initial tension to the said seal member at both ends.
For above reason, in gear pumps or motors of this type, both end parts of the figure-3 shaped seal member are kept just in touch with the inner wall surface of the gear bower in the housing to form the seal. As a result, during the operation of such gear pumps or motors, liquid in the high pressure zone at the back of the pressure plate may leak toward the low pressure zone through both end parts of the figure-3 shaped seal member. In other words, there is a defect in that the gear pump or motor suffers an impaired volumetric efficiency, that erosion is caused at the point of leakage, on the pressure plate or that the liquid pressure builds up in the low pressure zone, jeopardizing the pressure balance and giving rise to serious problems with respect to the performance and service life of the gear pump or motor.